1. Field of the Invention
The present invention relates to an improvement in a method of sterilization, and more particularly to an improvement in a sterilization method wherein rays emitted from a discharge lamp are applied to microorganisms to be destroyed.
2. Description of the Prior Art
One of the simple methods used heretofore for sterilization of microorganisms is irradiation by means of a sterilizer lamp.
Typical sterilizer lamps of the prior art are ones with power consumption of a few scores of watts. There are some lamps with power consumption of 200 watts or so, which, however, require a lamp length as much as 2 meters and thus do not provide a markedly increased dosage per unit arc length.
Among the large varieties of microorganisms for which the sterilizer lamp is used are those which readily absorb the rays, such as Aspergillus nigger. There is difficulty, however, in that when the microorganisms are present one upon another, the organisms in the lower layers are very hard to destroy in contrast to those in the upper layer. Thus, the conventional sterilizer lamp has the disadvantage that it requires a prolonged sterilization time or it attains only a limited sterilization rate for those organisms which readily absorb the rays, such as Aspergillus nigger.
Generally, the effectiveness of ultraviolet sterilization by means of the sterilizer lamp is given by: ##EQU1## where N.sub.0 and N are the number of organisms present before and after the ultraviolet irradiation, respectively,
e is the base of natural logarithm, PA1 P is a constant specific to the organism, PA1 I is the intensity of ultraviolet rays in the wavelength range effective for sterilizing the organisms, PA1 I.sub.0 is the intensity of the ultraviolet rays applied to the surface layer of the organisms, PA1 t is the irradiation time, PA1 .alpha. is the ultraviolet absorption factor of the organism, PA1 .beta. is a constant, and PA1 l is the distance of the lamp from the surface of the upper layer of the organisms.
It is evident from these expressions that effective sterilization is attained when sufficiently large values of I and t are used. Since .alpha. and .beta. are constants specific to the organism to be destroyed, the effectiveness of sterilization depends upon the value of I or t. The conventional sterilizer lamp which has a limited value of I.sub.0 and hence a similarly limited value of I must have recourse to an increased value of t, but is effective only in destroying the organisms present in the surface layer and exhibits a limited rate of sterilizing the organisms present one upon another.